Adhesion layer for multi-layer photoresist

ABSTRACT

A method is provided including forming a first layer over a substrate and forming an adhesion layer over the first layer. The adhesion layer has a composition including an epoxy group. A photoresist layer is formed directly on the adhesion layer. A portion of the photoresist layer is exposed to a radiation source. The composition of the adhesion layer and the exposed portion of the photoresist layer cross-link using the epoxy group. Thee photoresist layer is then developed (e.g., by a negative tone developer) to form a photoresist pattern feature, which may overlie the formed cross-linked region.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has generally increasedwhile geometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. However, such scaling down has also beenaccompanied by increased complexity in design and manufacturing ofdevices incorporating these ICs, and, for these advances to be realized,similar developments in device fabrication are needed.

In one exemplary aspect, photolithography (or simply “lithography”) is aprocess used in micro-fabrication, such as semiconductor fabrication, toselectively remove parts of a thin film or a substrate. The process usesradiation (e.g., light) to transfer a pattern (e.g., a geometricpattern) from a photomask to a light-sensitive layer (e.g., aphotoresist layer) on the substrate. Recently, advances such use of anextreme ultraviolet (EUV) radiation source have been utilized to providereduced feature sizes due to its short exposure wavelengths (e.g., lessthan 100 nm). Additional efforts have been made with the reduced featuresizes to improve photoresist, in some cases providing for thinner ormulti-layer resists. These advances in lithography and materials have insome embodiments been generally beneficial, they have not been entirelysatisfactory. For example, with reference to the photoresist poorcritical dimension uniformity, line edge roughness, photoresist featurecollapsing and/or increased defect counts have been encountered. Forthese reasons and others, additional improvements are desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 illustrates a flowchart of an exemplary method according tovarious aspects of the present disclosure.

FIGS. 2-12 are fragmentary cross-sectional views of an exemplary deviceat intermediate steps of an exemplary method according to variousaspects of the present disclosure.

FIGS. 13, 14, and 15 are also fragmentary cross-sectional views of anexemplary device at intermediate steps of an exemplary method andillustrate in further detail an interface provided in the exemplarymethod.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact ordirectly interfacing, and may also include embodiments in whichadditional features may be formed interposing the features, such thatthe features may not be in direct contact. In addition, spatiallyrelative terms, for example, “lower,” “upper,” “horizontal,” “vertical,”“above,” “over,” “below,” “beneath,” “up,” “down,” “top,” “bottom,” etc.as well as derivatives thereof (e.g., “horizontally,” “downwardly,”“upwardly,” etc.) are used for ease of the present disclosure of onefeatures relationship to another feature. The spatially relative termsare intended to cover different orientations of the device including thefeatures. Still further, when a number or a range of numbers isdescribed with “about,” “approximate,” and the like, the term isintended to encompass numbers that are within a reasonable rangeincluding the number described, such as within +/−10% of the numberdescribed or other values as understood by person skilled in the art.For example, the term “about 5 nm” encompasses the dimension range from4.5 nm to 5.5 nm.

The present disclosure relates generally to IC device manufacturing and,more particularly, to device patterning processes using a multi-layerphotoresist stack. However, one of ordinary skill in the art mayrecognize other implementations of certain embodiments of the adhesionlayer provided herein which would also be within the scope of thepresent disclosure.

Photoresist feature collapse plays a role in semiconductor fabricationincluding when the dimension of a semiconductor feature decreases to therange of 28 nanometers or less. Such collapse or peeling off of afeature impacts the reproduction of the pattern. Accordingly, thepresent disclosure provides a multi-layer photoresist stack andcorresponding fabrication methods that in some embodiments reduce forfeature collapse during lithography patterning processes by providingbeneficial adhesion between layers of the multi-layer photoresist.

FIG. 1 illustrates a flowchart of a method 100 for patterning a deviceaccording to some aspects of the present disclosure. The method 100 ismerely an example, and is not intended to limit the present disclosurebeyond what is explicitly recited in the claims. Additional operationscan be provided before, during, and after the method 100, and someoperations described can be replaced, eliminated, or moved around foradditional embodiments of the process. Intermediate steps of the method100 are described with reference to cross-sectional views of the device200 as shown in FIGS. 2-12 as well as FIGS. 13-15 providing additionalillustrations as to chemical structures formed at an interface providedin some embodiments of the method 100.

Referring to block 102 of FIG. 1, the method 100 provides (or isprovided with) a device including a substrate for patterning. Referringto the example of FIG. 2, the device 200 includes a substrate 202. Thesubstrate 202 may comprise an elementary (single element) semiconductor,such as germanium and/or silicon in a crystalline structure; a compoundsemiconductor, such as silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor such as SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,GaInP, and/or GaInAsP; a non-semiconductor material, such as soda-limeglass, fused silica, fused quartz, and/or calcium fluoride (CaF₂);and/or combinations thereof. The substrate 202 may be a single-layermaterial having a uniform composition; alternatively, the substrate 202may include multiple material layers having similar or differentcompositions suitable for IC device manufacturing. In one example, thesubstrate 202 may be a silicon-on-insulator (SOI) substrate having asemiconductor silicon layer formed on a silicon oxide layer. In otherexample, the substrate 202 may include conductive layers, semiconductorlayers, dielectric layers, other layers, and/or combinations thereof.

The substrate 202 may include various circuit features formed thereonincluding, for example, features associated with field effecttransistors (FETs), metal-oxide semiconductor field effect transistors(MOSFETs), CMOS transistors, high voltage transistors, high frequencytransistors, bipolar junction transistors, diodes, resistors,capacitors, inductors, varactors, other suitable devices, and/orcombinations thereof.

In some embodiments where the substrate 202 includes FETs, various dopedregions, such as source/drain regions, are formed on the substrate 202.The doped regions may be doped with p-type dopants, such as phosphorusor arsenic, and/or n-type dopants, such as boron or BF₂, depending ondesign requirements. The doped regions may be planar or non-planar(e.g., in a fin-like FET device) and may be formed directly on thesubstrate, in a P-well structure, in an N-well structure, in a dual-wellstructure, or using a raised structure. Doped regions may be formed byimplantation of dopant atoms, in-situ doped epitaxial growth, and/orother suitable techniques. In some embodiments, the substrate 202includes fin elements extending from a top surface upon which gates fora multi-gate FET (e.g., fin-like FETs) are formed. In an embodiment, thepatterned feature of a target layer 204 described below provides a gatestructure disposed over a fin as illustrated by certain aspects of FIGS.2-12, however, the present method 100 is not limited thereto. Further,in some embodiments, the method 100 may be used to form a maskingelement (e.g., FIG. 11) that is used to define regions of the substrate202 for further processing such as, ion implantation, epitaxial growth,deposition, and/or other suitable processes.

In some embodiments, the substrate 202 is alternatively a photomasksubstrate that may include a low thermal expansion material (LTEM) suchas quartz, silicon, silicon carbide, silicon oxide-titanium oxidecompound, and/or other suitable materials. For example, the substrate202 may be used to provide a photomask for deep ultraviolet (DUV)lithography, extreme ultraviolet (EUV) lithography, and/or otherlithography processes. The patterning process of the method 100 of FIG.1 may be used to form features on the photomask substrate for subsequentuse in lithography processes for forming semiconductor features on aseparate substrate.

Continuing with reference to the example of FIG. 2, illustrated is atarget layer 204 disposed over the provided substrate 202. It is notedthat in some embodiments, the substrate 202 itself is the target forprocessing using the pattern produced by the steps of the method 100.That is, for example, the target layer 204 is omitted. The target layer204 may have any composition suitable for processing in forming adevice. In some embodiments, the target layer 204 is a hard mask layerincluding compositions such as, amorphous silicon (a-Si), silicon oxide,silicon nitride (SiN), titanium nitride, and/or other suitablecompositions. In an embodiment, the target layer 204 may be ananti-reflective coating layer, a dielectric layer such as a high-kdielectric layer, a gate layer (e.g., polysilicon), a conductive layer,an interconnect layer such as interlayer dielectric (ILD) layers orconductive lines or vias, and/or various other layers and/or materialsused in the fabrication of semiconductor devices to which a patterningis desired. The target layer 204 may be formed over the substrate 202 byone or more deposition processes such as physical vapor deposition(PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD),spin-on coating, and/or other suitable deposition methods.

Referring to block 104 of FIG. 1, the method 100 continues to forming abottom layer of a multi-layer photoresist over the substrate. Referringto the example of FIG. 3, a bottom layer 206 is formed over thesubstrate 202 and the target layer 204 (if present). In an embodiment,the bottom layer 206 has an organic material composition. For example,the bottom layer 206 may include a composition of carbon (C), hydrogen(H), and/or oxygen (O). In some embodiments, the bottom layer 206 ispatternable (e.g., photosensitive). In some other embodiments, thebottom layer 206 is does not include a photosensitive material.

The bottom layer 206 may be formed by a suitable technique such asspin-on coating. The organic material composition of the bottom layer206 may be included in a solvent for deposition (e.g., spin-coating).Any suitable solvent may be used including, for example, n-butylacetate, methyl n-amyl ketone, 4-methyl-2-pentanol, propylene glycolmethyl ether acetate, propylene glycol methyl ether,gamma-butyrolactone, ethyl lactate, cyclohexanone, ethyl ketone,dimethyl formamide, alcohol (e.g., ethanol and methanol), other suitablesolvent, or combinations thereof. The solvent may be driven off bysubsequent baking processes (e.g., pre-exposure bake).

The bottom layer 206 may function to be a planarizing layer of themulti-layer photoresist (also referred to simply as resist) stack. Thebottom layer 206 may function to reduce the reflected light as ananti-reflective coating. Thus, in a further embodiment, the bottom layer206 may have a high n value and/or a low k value. The composition of thebottom layer 206 may also be selected such that it provides sufficientetch selectivity to the target layer 204 and/or the substrate 202 as insome embodiments, the bottom layer 206 may be used as a mask duringetching of the target layer 204/substrate 202.

One exemplary composition of the bottom layer 206 is a novolac resinsuch as provided by the chemical structure below where “n” denotes aninteger greater than or equal to 2.

Other compositions including other polymer compositions are possible forthe bottom layer 206. As discussed further below, the bottom layer 206is an under layer or bottom layer of a multi-layer patterning scheme(multi-layer resist). As stated above, the composition of the bottomlayer 206 may be selected such that the bottom layer 206 performs abottom anti-reflective coating (BARC) function whose composition ischosen to minimize reflectivity of a radiation source implemented duringexposure of a subsequently-formed photoresist layer. In someembodiments, the bottom layer 206 is deposited to a thickness of betweenapproximately 300 and 1500 angstroms (A). The bottom layer 206 may be aconformal layer as deposited.

The method 100 of FIG. 1 then proceeds to block 106 where a “middle”layer of a multi-layer photoresist patterning scheme is deposited.Referring to the example of FIG. 4, a middle layer 208 is formed overthe bottom layer 206. In some embodiments, the middle layer 208 directlyinterfaces the bottom layer 206. In other embodiments, other materialsmay interpose the middle layer 208 and underlying bottom layer 206.

The middle layer 208 may include a composition including silicon (Si),hydrogen (H), and/or oxygen (O). The middle layer 208 may be a siliconcontaining hard mask layer. In some embodiments, the middle layer 208 isa spin-on glass (SOG) film or silicate. For example, the middle layermay be SiO2. In other embodiments, the middle layer may include anitride such as silicon nitride or silicon oxynitride.

In some embodiments the middle layer 208 is formed by spin-ondeposition. However, other suitable deposition methods are alsopossible. Exemplary thicknesses of the middle layer 208 include, but arenot limited to, approximately 30 to 300 angstroms.

As stated above, the bottom layer 206 and the middle layer 208 mayprovide two layers of a multi-layer resist stack. In someimplementations of a tri-layer resist formulation, a photosensitivelayer is disposed directly on top of the middle layer of the tri-layerresist. However, the intrinsic difference in structure between theoverlying photoresist composition and the middle layer of the tri-layerresist formulation can provide a point of weakness. This weakness if notmitigated can lead to the overlying photoresist features undesirably“peeling off” from the middle layer.

Thus, the method 100 of FIG. 1 advantageously proceeds to block 108where an adhesion layer (also referred to as a coating) is formed overthe middle layer. In some embodiments, the adhesion layer is disposeddirectly on the middle layer. The adhesion layer maybe a conformalcoating. Further, the adhesion layer may have a direct interface withthe overlying photoresist layer as described below. Referring to theexample of FIG. 5, an adhesion layer 210 is disposed over the middlelayer 208.

The adhesion layer 210 includes a polymer composition including an epoxygroup (also referred to as an epoxide functional group) attached to thepolymer. An epoxy group is a cyclic ether with a three atom ring, whichis highly reactive due to the strain of the ring. A chemical schematicrepresentation of the epoxy group is provided below where R1 or R2provides the bonding to the polymer backbone and the other of R1 or R2is H or any other suitable component.

In an embodiment, the adhesion layer 210 includes silicon based polymerhaving the epoxy functional group bonded thereto. For example, in someembodiments, the adhesion layer may include a siloxane polymer with anepoxy group bonded thereto. For example, the following structure may beprovided showing the siloxane polymer backbone (with n and m greaterthan 0), and the epoxy group attached thereto:

In some examples, m is equal to between approximately 40 and 90. In someexamples, n is equal to between approximately 10 and 60.

In some embodiments, the adhesion layer 210 is deposited by aspin-coating process. The spin-coating process may be implemented bydepositing a polymer (having the epoxy functional group) dissolved in asuitable solvent over the substrate 202. The spin-coating may includerotating the substrate 202 to cause the polymer (having the epoxyfunctional group) to form a thin coating providing the adhesion layer210 across a top surface of or above the substrate 202. Any suitablesolvent may be used including, for example, n-butyl acetate, methyln-amyl ketone, 4-methyl-2-pentanol, propylene glycol methyl etheracetate, propylene glycol methyl ether, gamma-butyrolactone, ethyllactate, cyclohexanone, ethyl ketone, dimethyl formamide, alcohol (e.g.,ethanol and methanol), other suitable solvent, or combinations thereof.It is noted that subsequently, the solvent is evaporated by baking(i.e., curing) to form the adhesion layer 210.

In some embodiments, a thickness of the adhesion layer 210 is betweenapproximately 50 Angstroms and approximately 100 Angstroms. It is notedthat the thickness may affect subsequent etching processes (e.g.,patterning of the middle layer 208) and as such should be controlled asdiscussed below.

The method 100 then proceeds to block 110 where a photoresist layer isformed on the adhesion layer. Using the example of FIG. 6, a photoresistlayer 212 is formed over the adhesion layer 210. It is noted that thestack of the bottom layer 206, the middle layer 208, and the photoresistlayer 212 and including the interposing adhesion layer 210 form amulti-layer resist stack 214 to be used for a patterning scheme for thesubstrate 202 and/or target layer 204. The photoresist layer 212 may beany lithographically sensitive resist material, and in many embodiments,the photoresist layer 212 includes a photoresist material sensitive to aradiation source (e.g., UV light, deep ultraviolet (DUV) radiation,and/or EUV radiation as depicted in FIG. 7). However, the principles ofthe present disclosure may also apply to e-beam resists and otherdirect-write resist materials. In one embodiment, the photoresist layer212 includes a resist material that polymerizes (and/or crosslinks) andsubsequently becomes more insoluble in a developer after the resistmaterial is exposed to a radiation source. The photoresist layer 212 maybe a negative tone development (NTD) resist, i.e., its solubility in adeveloper decreases upon the radiation. An example of the resist used inan NTD process is a polymeric material including cross-linkable polymerand cross-linkers, where the polymer molecules of the resist itselfcross-link upon radiation. It is noted that this cross-linking withinthe photoresist layer 212 itself (i.e., by the polymer provided asphotoresist layer 212) is separate and distinct from the cross-linkingwith the epoxy group of the adhesion layer 210 that is discussed below.

The photoresist layer 212 includes a polymer having photosensitivefunctional groups such as, for example, a photo-acid generator (PAG), athermal-acid generator (TAG), a photo-base generator (PBG), aphoto-decomposable base (PDB), a photo-decomposable quencher (PDQ), orother photosensitive functional groups. Exemplary photoresistcompositions include resists sensitive to a radiation, such as an I-linelight, a DUV light (e.g., 248 nm radiation by krypton fluoride (KrF)excimer laser or 193 nm radiation by argon fluoride (ArF) excimerlaser), a EUV light (e.g., 13.5 nm light), an e-beam, an x-ray, and anion beam. For example, an exemplary KrF sensitive resist composition andArF sensitive resist composition are provided below where x and y and a,b and c are any integer greater than 1.

The photoresist layer 212 may also include a solvent(s) on depositionthat are subsequently driven off as part of the spin coating, during asettling process, and/or during a post-application/pre-exposure bakingprocess. The pre-exposure baking process may be implemented by anysuitable equipment such as, for example, a hotplate, at any temperaturesuitable for the particular compositions of the photoresist layer 212and the solvent(s) employed.

The method 100 then proceeds to block 112 where an exposure process isperformed. The exposure process may be performed by a system employingdeep ultraviolet (DUV) lithography, extreme ultraviolet (EUV)lithography, electron beam (e-beam) lithography, x-ray lithography, ionbeam lithography, and other lithography processes. Referring to block112 of FIG. 1 and to the example of FIG. 7, the method 100 exposes thephotoresist layer 212 to the radiation 702. In some embodiments, theradiation 702 is provided from a source that provides an I-line(wavelength approximately 365 nm), a DUV radiation such as KrF excimerlaser (wavelength approximately 248 nm) or ArF excimer laser (wavelengthapproximately 193 nm), a EUV radiation (wavelength from about 1 nm toabout 100 nm), an x-ray, an e-beam, an ion beam, and/or other suitableradiations. The exposure process providing the radiation 702 may beperformed in air, in a liquid (immersion lithography), or in vacuum(e.g., for EUV lithography and e-beam lithography). In the depictedembodiment, the exposure process at block 112 and the example of FIG. 7implements a photolithography technique using a photomask 704 thatincludes a pattern providing the opening for radiation 702 to becomeincident the device 200. The photomask 704 may be a transmissive mask ora reflective mask, the latter of which may further implement resolutionenhancement techniques such as phase-shifting, off-axis illumination(OAI) and/or optical proximity correction (OPC). In alternativeembodiments, the radiation 702 is patterned directly without using aphotomask 704 (such as using a digital pattern generator or direct-writemode). In an embodiment, the radiation 702 is a EUV radiation and theexposure process at block 112 is performed in a EUV lithography system.Correspondingly, a reflective photomask 704 may be used to pattern thephotoresist layer 212.

As depicted in FIG. 7, regions 212 a of the photoresist layer 212 areexposed to the radiation 702; these exposed regions 212 a undergochemical changes while unexposed regions remain substantially unchangedin chemical properties. Accordingly, following the exposure process atblock 112, in the embodiment of a NTD resist, the exposed regions 212 aof the photoresist layer 212 undergo polymerization and/or crosslinkingof the resist material and may become less soluble to a subsequentlyapplied developer as a result. The exposure to the radiation 702 mayalso in some embodiments provide for some cleaving of an acid leavinggroup in the exposed region 212 a as discussed below.

The method 100 then proceeds to block 114 where a post exposure bake(PEB) is performed. The PEB may include baking the device 200 afterblock 112 is completed. In an embodiment, the PEB is performed betweenapproximately 150 and approximately 350 degrees Celsius. Thepost-exposure baking process may catalyze any chemical reactioninitiated by the exposure process at block 112 within the photoresistlayer 212, and also between the exposed photoresist layer 212 andadhesion layer 210 as discussed below. For example, the post-exposurebaking process may accelerate a cleaving of the acid labile group,accelerate the crosslinking within the photoresist layer 212, and/oraccelerate the crosslinking between the photoresist layer 212 and theadhesion layer 210.

Referring still to the method 100 of FIG. 1, provided in block 116 ofthe method 100 is a cross-linking between the adhesion layer and theoverlying photoresist layer occurs. The cross-linking forms across-linked region between the adhesion layer and upper portions of theexposed photoresist layer. Block 116 may occur after and/or concurrentlywith block 112 of the method 100. Additionally or alternatively, block116 may occur concurrently with block 114 of the method 100 and/orresult from the process of block 114. In other words, the cross-linkingbetween the adhesion layer and the photoresist layer may develop at thetime of exposure and/or be facilitated by the PEB.

As an example of the cross-linking between the exposed photoresist andthe adhesion layer, in an embodiment, the photoresist layer 212 includesa polymer having an acid labile group. In some embodiments, the acidlabile group molar ratio in the polymer is between approximately 20% andapproximately 70%. The percentage of acid labile group molar ratio canaffect the extent of the cross-linking as it affects the —COOHfunctional groups produced which in turn affect the extent ofcross-linking as discussed below. During and/or after exposure of thephotoresist layer 212, the composition of the exposed portions of thephotoresist 212 a undergo a cleaving of the acid labile group generating—COOH (carboxylic acid) functional groups. The —COOH functional groupnow attached to the polymer of the exposed portion 212 a of thephotoresist can cross-link with the available epoxy group of theadhesion layer 210. Adjusting the loading of —COOH functional group thatwill be produced on the polymer backbone of the exposed region 212 a maytune the cross-linkability of the photoresist layer 212 to the adhesionlayer 210. That is, in some embodiments, adjusting the acid labile groupmolar ratio affects the extent of cross-linking.

In an embodiment, a crosslinking region 600 is created by the bonding(cross-linking) of the adhesion layer (epoxy group) and the photoresistlayer 212 (the —COOH group). The crosslinking region 600 may be disposedon the adhesion layer 210. In some embodiments, the crosslinking region600 extends approximately 15 angstroms into the photoresist layer 212.Further discussion of block 116 and the resulting crosslinking region,such as illustrated by crosslinking region 600, is provided withreference to FIGS. 13-15 discussed below.

Continuing with the method 100 of FIG. 1, the method 100 proceeds toblock 118 where the now-exposed photoresist layer is developed.Referring to the example of FIGS. 7 and 8, the photoresist layer 212including exposed photoresist region 212 a is introduced to a developerto form a resist pattern illustrated as resist pattern feature 212 b inFIG. 8. In an embodiment, a negative tone developer (NTD) is applied. Inan embodiment, the developer applied includes an organic solvent havinga Log P value greater than 1.82. See U.S. Pat. No. 9,459,536 whichdescribes a suitable developer and is hereby incorporated by referencein its entirety. The developer may include an aqueous solvent or anorganic solvent. Suitable organic-based developers include n-butylacetate, ethanol, hexane, benzene, toluene, and/or other suitablesolvents, and suitable aqueous developers include aqueous solvents suchas tetramethyl ammonium hydroxide (TMAH), KOH, NaOH, and/or othersuitable solvents. In cases wherein a NTD resists and developers areused, as illustrated in FIGS. 7 and 8, the exposed portion 212 a of thephotoresist layer 212 are maintained while the unexposed portions areremoved thereby forming one or more openings in the photoresist layer212. It is noted that the crosslinking region 600 remains within theresist pattern 212 b.

The method 100 then proceeds to block 120 where etching process(es) areperformed while using masking elements resist pattern provided by thedeveloped photoresist discussed above, and/or patterns provided in theunderlying layers using the developed photoresist. Using FIG. 9 asexemplary, the middle layer 208 is etched using the patterned resistfeature 212 b feature. In some embodiments, the same etching processused to pattern the middle layer 208 also (substantially concurrently)patterns the adhesion layer 210 thereby providing patterned middle layer208 a and patterned adhesion layer 210 a in a single etching processusing the patterned resist 212 b as masking element during the singleetching process. It is noted that the composition and thickness of theadhesion layer 210 are to be considered in the formation of thepatterned adhesion layer 210 a. If the adhesion layer 210 includes acarbon based material, the patterned adhesion layer 210 a may need to berelatively thinner in order to not impact the ability to use a singleetching step for the adhesion layer 210 and the middle layer 208. If theadhesion layer 210 is a silicon based layer as well as the middle layer208 being a silicon based layer the single etching step may be morequickly facilitated should the compositions provide similar etchingrates. In some embodiments, the thickness of the adhesion layer 210 isbetween approximately 50 Angstroms and 100 Angstroms. In an embodiment,the adhesion layer has an epoxy group, which provides for a highercarbon percentage and a lower etch rate (relative to the middle layer)during the middle layer etching by suitable etchant (e.g., CF4 gas). Athinner adhesion layer therefore may be desirable. In contrast to thisdesire for a thin adhesion layer, there may be concerns of fabricatingthe layer (e.g., bubbles) if the thickness is too low (e.g., below 50Angstroms).

Block 120 may continue to process underlying layers. For example, insome embodiments, subsequent to forming the patterned middle layer 208a, the patterned middle layer 208 a is used as masking element duringthe subsequent etching process(es) directed at the bottom layer 206.During the etching of the bottom layer 206, the masking element mayinclude the patterned middle layer 208 a and the patterned adhesionlayer 210 a disposed thereon. This etching step of the bottom layer 206may be separate from (e.g., using different etchants) than the etchingstep used to provide the patterned middle layer 208 a. The resistpattern 212 b may be partially consumed or fully consumed during theetching of the bottom layer 206. Se FIG. 10. The method 100 may have anoptional operation to strip off the remaining portions of the resistpattern 212 b after forming the patterned middle layer 208 a. Forexample, the resist pattern 212 b is subsequently removed using anysuitable method such as, for example, by plasma ashing or flushing usingoxygen and/or nitrogen plasma.

The etching thus provides a patterned bottom layer 206 a having thepatterned middle layer 208 a disposed thereon. In some embodiments, thepatterned adhesion layer 210 a is also disposed over the patternedbottom layer 206 a and patterned middle layer 208 a as illustrated inFIG. 11. The crosslinking region 600 may also continue to be disposed onthe masking element including the patterned middle layer 208 a. In otherembodiments, the crosslinking region 600 may be removed simultaneouslywith the photoresist pattern feature 212 b.

The method 100 then proceeds to block 122 where continued fabrication isperformed. The continued fabrication may use the masking elementincluding the patterned middle layer, patterned bottom layer, and/orpatterned adhesion layer. As illustrated in FIGS. 11 and 12, thepatterned bottom layer 206 a, the patterned middle layer 208 a, and/orthe patterned adhesion layer 210 a are used as a masking element duringthe etching of the target layer 204 creating patterned target layer 204a. In some embodiments, the patterned middle layer 208 a and patternedadhesion layer 210 a are removed and the patterned bottom layer 206 a isused as a masking element. In other embodiments, in addition to or inlieu of an etching process, any suitable method may be performed toprocess the substrate 202 using the patterned bottom layer 206 a, thepatterned middle layer 208 a, and/or the patterned adhesion layer 210 aas a masking element including additional etching process, a depositionprocess, an implantation process, an epitaxial growth process, and/orany other fabrication process.

The etching of block 120 and/or block 122 may be accomplished using anysuitable method including a dry etching process, a wet etching process,other suitable etching process, a reactive ion etching (RIE) process, orcombinations thereof. In an exemplary embodiment, a dry etching processis implemented and employs an etchant gas that includes anoxygen-containing gas (e.g., O₂), a carbon-containing gas (e.g.,C_(x)H_(y), where x and y may be any integers), a fluorine-containingetchant gas (e.g., C_(x)F_(y), C_(x)H_(y)F_(z), N_(x)F_(y), and/orS_(x)F_(y), where x, y, and z may be any integers), achlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃), abromine-containing gas (e.g., HBr and/or CHBR₃), an iodine-containinggas, other suitable gases and/or plasmas, and/or combinations thereof.

In some embodiments, the bottom layer 206 is a photosensitive layer.Therefore, the method 100 (FIG. 1) may include performing additionalexposing process(es) to the bottom layer 206 through openings of themasking element including patterned middle layer 208 a. By using tworesist layers and double exposing process, the fidelity of the processwindow may be improve and a smaller critical dimension may be achieved.

Although not shown in FIG. 1, the method 100 may proceed to furtherprocesses in order to form a final pattern or device. For example, themethod 100 may etch the substrate 202 with the target layer 204 as anetch mask. For another example, the method 100 may deposit additionallayer(s) above the target layer 204 and perform patterning processes tothe additional layer(s). For example, the method 100 may form shallowtrench isolation (STI) features for defining transistor active regions,may form fin-like protrusions in the respective substrates for formingFinFETs, may form contact holes for transistor source/drain/gatecontacts, and may form interconnect features.

The device 200 may then be provided for additional fabricationprocesses. For example, the device 200 may be used to fabricate anintegrated circuit chip, a system-on-a-chip (SOC), and/or a portionthereof, and thus the subsequent fabrication processes may form variouspassive and active microelectronic devices such as resistors,capacitors, inductors, diodes, metal-oxide semiconductor field effecttransistors (MOSFET), complementary metal-oxide semiconductor (CMOS)transistors, bipolar junction transistors (BJT), laterally diffused MOS(LDMOS) transistors, high power MOS transistors, other types oftransistors, and/or other circuit elements.

Referring again to blocks 108, 110, 112, 114, and 116 of the method 100of FIG. 1, further description is provided with reference to FIGS. 13,14, and 15 detailing exemplary crosslinking provided between theadhesion layer and the overlying photoresist layer. FIG. 13 issubstantially similar to a portion of FIG. 5 illustrating the adhesionlayer 210 formed over the middle layer 208, each described in detailabove. FIG. 13 illustrates that a top surface of the adhesion layer 210includes available epoxy ring 1002 available for bonding. As explainedabove, the epoxy ring 1002 may be a functional group attached to apolymer of the adhesion layer 210. The epoxy ring 1002 is highlyreactive due to the stress of the three element ring. Example backboneof the polymer is illustrated below and the epoxy ring 1002 attached.

In some embodiments, m is between approximately 40 and 90 and n isbetween approximately 10 and 60. In some embodiments, m is greater thann.

FIG. 14 is illustrative of subsequent processing of the device includingblocks 112, 114, and 116 where a photoresist layer 212 is disposed overthe adhesion layer 210, an exposure process is performed introducingradiation 702 that creates exposed photoresist region 212 a, each ofwhich is described above with reference to the method 100 and exemplaryFIGS. 6-7. Illustrated by FIG. 14 is the exemplary cross-linking betweenthe exposed resist portion 212 a and the underlying adhesion layer 210.Namely, the epoxy ring of the adhesion layer 210 is opened and aphotoresist component is cross-linked to the opened epoxy ring. In someembodiments, the exposed photoresist region 212 a undergoes a cleavingof an acid labile group attached to the polymer. The cleaving of theacid labile group generates —COOH (carboxylic acid) functional groups.This —COOH functional group can cross-link with the available epoxygroup of the adhesion layer 210. The baking process of block 114 mayfurther advance this cross-linking. The thickness Tx of the cross-linkedregion 600 can be approximately 15 Angstroms. In some embodiments, thethickness Tx of the cross-linked region 600 can be between approximately5 Angstroms and approximately 25 Angstroms. It is noted that nocross-linking may occur in the portions of the photoresist layer 212 notsubject to the exposure by radiation 702. FIG. 15 is illustrative of thephotoresist layer 212 after development and removal of the non-exposedportions of the photoresist layer 212. The cross-linked region 600remains.

Although not intended to be limiting, one or more embodiments of thepresent disclosure provide many benefits to a semiconductor device and aformation process thereof. For example, embodiments of a multi-layerphotoresist structure including an adhesion layer offers greater controlover the lithographic patterning process by mitigating a risk ofphotoresist peeling. As a result, opportunities forming photoresistfeatures with sufficient aspect ratio may be afforded by embodimentsprovided herein.

In an embodiment, a method is provided that includes forming a firstlayer over a substrate. An adhesion layer is formed over the firstlayer. The adhesion layer has a composition including an epoxy group. Aphotoresist layer is formed directly on the adhesion layer. A portion ofthe photoresist layer is exposed to a radiation source. The compositionof the adhesion layer and the exposed portion of the photoresist layerare cross-linked. The epoxy group provides the cross-linking. Thephotoresist layer is developed to form a photoresist pattern feature.

In a further embodiment, the adhesion layer is formed by spin-coatingthe composition. In an embodiment, the composition of the adhesion layeris a silicon based polymer with the epoxy group. In a furtherembodiment, composition of the adhesion layer is a siloxane polymer withthe epoxy group. In an embodiment, the cross-linking creates across-linked region of the photoresist layer. The cross-linked region isbetween a portion of the exposed photoresist and the adhesion layer. Inan embodiment, the radiation source is an extreme ultra-violet (EUV)wavelength radiation source. In an embodiment, developing thephotoresist layer includes providing a negative-tone developer. In anembodiment, forming the first layer over the substrate includesdepositing a second composition including silicon, oxygen and hydrogen.

In another of the broader examples, a method includes forming a firstlayer over a substrate. An adhesion layer is formed over the firstlayer. The adhesion layer includes a polymer having an epoxy functionalgroup. A photoresist layer is formed directly on the adhesion layer. Themethod includes using an extreme ultraviolet (EUV) radiation source toexpose the photoresist layer, the exposed photoresist layer is baked.During at least one of the exposing or the baking, the epoxy functionalgroup of the adhesion layer is cross-linked to the exposed photoresistlayer creating a cross-linked region between a portion of the exposedphotoresist layer and the adhesion layer. The method continues to applya negative tone developer (NTD) to develop the photoresist layer to forma photoresist pattern feature, wherein the cross-linked region underliesthe photoresist pattern feature. A first etching process is performedwhile using the photoresist pattern feature as an etch mask to form apatterned first layer, wherein the first etching process removesportions of the adhesion layer disposed over the first layer.

In a further embodiment, the method includes performing a second etchingprocess using the patterned first layer to etch an underlying layer. Inan embodiment, the underlying layer is an anti-reflective coating layer.In an embodiment, the adhesion layer includes a siloxane polymer withthe epoxy functional group attached. In an embodiment, the adhesionlayer is a spin coated conformal layer. In an embodiment, the epoxyfunctional group of the adhesion layer is cross-linked to the exposedphotoresist layer by an opening of the epoxy functional group. In anembodiment, the epoxy functional group bonds with a —COOH functionalgroup of the exposed photoresist layer. The —COOH functional group maybe generated by cleaving of an acid labile group during the exposing.

In yet another of the broader embodiments described is a methodincluding forming a hard mask layer over a substrate and spin-coating anadhesion layer over and directly interfacing the hard mask layer. Aphotoresist layer is then formed over and directly interfacing theadhesion layer. A first region of the photoresist layer is exposed. Themethod includes forming a cross-linked region between the adhesion layerand the first region of the photoresist layer. A negative tone developeris used to develop the photoresist layer to form a photoresist patternfeature over the cross-linked region.

In a further embodiment, the adhesion layer includes a polymer having anepoxy functional group. In an embodiment, the hard mask layer includessilicon, oxygen, and hydrogen. In an embodiment, the forming thephotoresist layer includes forming a polymer providing at least one of aKrF sensitive resist composition or ArF sensitive resist composition.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a first layer over asubstrate; forming an adhesion layer over the first layer, wherein theadhesion layer has a composition including an epoxy group; forming aphotoresist layer directly on the adhesion layer; exposing a portion ofthe photoresist layer to a radiation source; cross-linking thecomposition of the adhesion layer and the exposed portion of thephotoresist layer, wherein the epoxy group provides the cross-linking;and developing the photoresist layer to form a photoresist patternfeature.
 2. The method of claim 1, wherein the forming the adhesionlayer includes spin-coating the composition.
 3. The method of claim 1,wherein the composition of the adhesion layer is a silicon based polymerwith the epoxy group.
 4. The method of claim 3, wherein the compositionis a siloxane polymer with the epoxy group.
 5. The method of claim 1,wherein the cross-linking creates a cross-linked region of thephotoresist layer, wherein the cross-linked region between a portion ofthe exposed photoresist and the adhesion layer.
 6. The method of claim1, wherein the radiation source is an extreme ultra-violet (EUV)wavelength radiation source.
 7. The method of claim 1, wherein thedeveloping the photoresist layer includes providing a negative-tonedeveloper.
 8. The method of claim 1, wherein the forming the first layerover the substrate includes depositing a second composition includingsilicon, oxygen and hydrogen.
 9. A method, comprising: forming a firstlayer over a substrate; forming an adhesion layer over the first layer,wherein the adhesion layer includes a polymer having an epoxy functionalgroup; forming a photoresist layer directly on the adhesion layer; usingan extreme ultraviolet (EUV) radiation source, exposing the photoresistlayer; baking the exposed photoresist layer; wherein during at least oneof the exposing or the baking, the epoxy functional group of theadhesion layer is cross-linked to the exposed photoresist layer creatinga cross-linked region between a portion of the exposed photoresist layerand the adhesion layer; applying a negative tone developer (NTD) todevelop the photoresist layer to form a photoresist pattern feature,wherein the cross-linked region underlies the photoresist patternfeature; and performing a first etching process while using thephotoresist pattern feature as an etch mask to form a patterned firstlayer, wherein the first etching process removes portions of theadhesion layer disposed over the first layer.
 10. The method of claim 9,further comprising: performing a second etching process using thepatterned first layer to etch an underlying layer.
 11. The method ofclaim 10, wherein the underlying layer is an anti-reflective coatinglayer.
 12. The method of claim 9, wherein the adhesion layer includes asiloxane polymer with the epoxy functional group attached.
 13. Themethod of claim 9, wherein the adhesion layer is a spin coated conformallayer.
 14. The method of claim 9, wherein the epoxy functional group ofthe adhesion layer is cross-linked to the exposed photoresist layer byan opening of the epoxy functional group.
 15. The method of claim 9,wherein the epoxy functional group bonds with a —COOH functional groupof the exposed photoresist layer.
 16. The method of claim 15, whereinthe —COOH functional group is generated by cleaving of an acid labilegroup during the exposing.
 17. A method, comprising: forming a hard masklayer over a substrate; spin-coating an adhesion layer over and directlyinterfacing the hard mask layer; forming a photoresist layer over anddirectly interfacing the adhesion layer; exposing a first region of thephotoresist layer; forming a cross-linked region between the adhesionlayer and the first region of the photoresist layer; and using anegative tone developer, developing the photoresist layer to form aphotoresist pattern feature over the cross-linked region.
 18. The methodof claim 17, wherein the adhesion layer includes a polymer having anepoxy functional group.
 19. The method of claim 17, wherein the hardmask layer includes silicon, oxygen, and hydrogen.
 20. The method ofclaim 17, wherein the forming the photoresist layer includes forming apolymer providing at least one of a KrF sensitive resist composition orArF sensitive resist composition.